The U.S. dollar chalked up strong gains on all major foreign exchange markets yesterday reflecting U.S. gold sales and an agreement by major central banks not to sell dollars.

Gold weakened in Europe, but was a bit higher at the close in New York. In Zurich gold closed at $373.50, down from its Friday close of $375.50. In London gold closed at $374, down from Friday's $375.50 and in New York it was a bit stronger at the close of commodtiy exchanges at $375 an ounce.

In Frankfurt the dollar closed at 1.8120 marks, up from 1.8040 at Friday's close; in Zurich at 1.6805 Swiss francs, up from 1.66675; in Brussels at 29.94 Belgian francs against 29.83; in Amsterdam at 2.013 guilders against 2.0055 and in Milan at 834.30 lire, up from 831.05. $

In London the pound fell to $2.0960 from Friday's close of $2.1045. In Tokyo, the dollar closed at 234.75 yen, fractionally up on Friday's 234.70. In New York the dollar closed at 1.8096 German marks, 1.7890 Swiss francs, 29.15 Belgian francs, 2.01 Dutch guilders. 833.40 Italian lire, 4.2335 French francs.